Machine for multiple grinding of semiconductor

ABSTRACT

A machine for multiple grinding blanks of crystalline structure in the production of semiconductors. It accomplishes the cuttingoff, grinding and polishing operations. The machine comprises a turn table on which there are mounted carriages with blanks. Around the table there are mounted grinding heads. The process of machining blanks is carried out continuously by way of successive steps of grinding and polishing the ends of blanks and then cutting-off the latter.

United States Patent [191 Dolgov et a1.

MACHINE FOR MULTIPLE GRINDING OF SEMICONDUCTOR Inventors: ValentinMikhailovich Dolgov, ulitsa Ljublinskaya, 23, kv. 21; VyacheslavVasilievich Saveliev, Anadyrsky proezd, 67, kv. 48; VladimirKonstantinovich Krylov, Yaroslavskoe shosse, 131, kv. 3; ValentinMitrofanovich Tomashevsky, 3 Mytischinskaya ulitsa, 14a, kv. 140; EvgenyIvanovich Zolotarev, ulitsa Kibalachicha, 15, kv. 12, all of Moscow,U.S.S.R.

Filed: Nov. 8, 1972 Appl. No.: 304,834

U.S. Cl. 51/5 B, 51/58, 5-1/215 AR,

51/215 UE Int. Cl B24b 7/04 Field of Search 51/3, 4, 5, 53, 55,133,

51/134, 215 AR, 215 UE, 216 T, 216 ND; 269/57; l25/DIG. 1

Primary Examiner-AlLawrence Smith Assistant ExaminerRobert C. WatsonAttorney, Agent, or FirmWaters, Roditi, Schwartz & Nissen [57] ABSTRACTA machine for multiple grinding blanks of crystalline structure in theproduction of semiconductors. lt accomplishes the cutting-off, grindingand polishing operations. The machine comprises a turn table on whichthere are mounted I carriages with blanks. Around the table there aremounted grinding heads.

The process of machining blanks is carried out continuously by way ofsuccessive steps of grinding and polishing the ends of blanks and thencutting-off the latter.

5 Claims, 4 Drawing Figures 6 a a i o it 6'4 t 0 as 5 r Patented Jan. 7,1975 3,858,369

4 Sheets-Sheet 2 Patented "Jan. 7, 1975 4' Sheets-Shet 4 MACHINE FORMULTIPLE GRINDING OlF SEMICONDUCTOR The present invention relates to theproduction of semi-conductor devices, and more particularly, to amachine for grinding materials having, for example, crystallinestructures such as silicon, germanium, gallium arsenide, sitall, quartzand ceramics suitable for the production of solar phototransducers,integrated circuits, diodes, triodes, resistors, and detectors.

The process of machining such materials is characterized in that theblanks are first cut on machines with diamond abrasive discs into platesof necessary thick ness, and the plates are then ground and polished onface grinding-polishing machines with the use of abrasive pastes ordiamond lapping wheels.

Known in the art are devices for cutting and polishing materials ofcrystalline structure.

The known method for machining materials of crystalline structure withthe use of these devices is characterized in that a blank is glued to aholder and cut into plates which are then ground and polished. Thismethod, which is accomplished with the use of the known devices, doesnot provide a high productivity of labour due to the losses in time forauxiliary operations such as reloading of the devices in the process ofcutting blanks into plates, when a blank cut into plates should beremoved from the holder, washed and transported for a subsequentprocessing of grinding. Before grinding, the plates are glued to discsand ground to be flattened in the same plane, then the discs with theplates are washed to remove abrasive particles and chips; the initialthickness is measured, they are transported for a subsequent operationof polishing. The polishing is accomplished with the use of abrasives orpolishing wheels in a number of steps by reducing the granularity gradeof the abrasives and wheels; subse quent to each of the polishing steps,the discs with the plates are washed and the thickness of the removedlayer is measured. On completion of grinding, the plates are removedfrom the discs and washed of the glue.

The machining of blanks with the use of the known devices inevitablyresults in losses of the material being treated, since the cutting ofblanks into plates produces a spread in the thickness of the cut platesdue to pulsations of the cutting-off head. Therefore, the plates shouldbe ground for levelling in thickness which results in the losses ofexpensive materials in the form of chips.

There are known machines for cutting semiconductors with diamondabrasive discs, e.g., of the Staxs type (FRG).

The known machine comprises a bed with a body mounted thereon for aspindle assembly carrying a cutting head with a diamond abrasive discwhich is able to cut blanks, for example, of silicon and germanium 60 mmin diameter. The holder with a blank is fixed on a table capable ofmoving longitudinally and transversely because of a pushing fork and aneccentric in the tablereturning mechanism. The cutting head with adiamond disc is rotated from a belt drive provided with a governor ofrotation velocity in the range from 1,500 to 5,000 r.p.m. The cutting ofblanks into measured plates is accomplished by delivering the table withthe holder carrying a blank to the cutting edge of the diamond disc.

The advantage of such machines is in an improved stiffening of thediamond disc to the cutting head which provides a reduction of discvibrations while processing, the wastes of the material being cut areconsiderably reduced due to a small thickness of diamond discs; thesurface damage of plates is minor as compared to the other methods ofcutting.

The disadvantage of this device is the necessity of frequent reloadings.Besides, there should be provided special polishing devices forsubsequent processings of cut off blank plates.

There are known face grinding-polishing machines for grinding andpolishing semiconductor materials provided with a spindle for fasteninga polishing tool and a round table. The spindle has an electric drivewith a rotation velocity control in the range from 50 to 800 r.p.m. Thetable for plates to be glued thereon for processing is provided with anelectric drive equipped with rotation velocity control. The advantage ofsuch devices is their high grind precision but they are disadvantageousbecause of a low productivity of labour.

Therefore, an increase of the productivity of labour in grindingsemiconductor blanks can be provided only by a considerable increase inthe number of cuttinggrinding and polishing devices now in use.

An object of this invention is to increase productivity of labour inmachining materials of crystalline structure.

Another object of this invention is to reduce wastes of the materialbeing treated.

Yet another object of the present invention is to provide reduction offloor areas occupied for accomplishing the machining processes.

Still further object of the invention is to provide a reduction of theproduction cost.

These and other objects are attained by providing a machine for multiplegrinding of semiconductor blanks comprising a bed with a turn tablemounted thereon, on which turn table there are secured rotary chuckswith blanks, machining heads including grinding heads and polishingheads which are located around the periphery of the table and are madeto rotate about their axes and to move along the grinding plane, inwhich, according to the present invention, there are provided rotarycutting-off heads, which are so positioned that they can oscillate alongthe grinding plane between the grinding heads and the polishing headsand the travel of which constitutes an oscillatory motion, while on thetable which is mounted with a provision for a circular stepped feed,there are located carriages radially reciprocating with respect to themachining heads, each of the carriages carrying said chuck with blanksand a pusher for delivering said blanks to the cutting-off heads.

It is advisable that the cutting-off head he manufactured in the form ofa hollow shaft with a transporting means mounted therein in such a waythat the blank could be introduced, when it is being cut, into thecutting-off head and then the cut-off portions of the blank be fed tothe transporting means.

It is advantageous that the bed he provided with a rack fixed thereonand the carriage be provided with a screw having a gear which, as thetable is turned, could be engaged with the rack and, as the screw isrotated, the carriage with blanks could be moved to the cuttingoff headsfor a specified distance of cutting.

The present invention in accordance with one of the variants of itsembodiment may be provided with hollow shafts located in the bed, towhich shafts there are fixed link gears for imparting oscillating motionto said heads the drive shaft of which is located inside of the hollowshaft.

The present invention provides simultaneous processes of polishing andcutting a large number of blanks and a reliable transportation ofcut-off plates from the cutting zone. This provides a considerableincrease in the productivity of labour.

Besides, the wastes of the material produced in the machining processeshave been reduced.

The following example illustrates a specific embodiment of the presentinvention with reference to the accompanying drawings, wherein:

FIG. 1 is a plan view of the machine according to the invention;

FIG. 2 is a vertical section of the grinding head;

FIG. 3 is a vertical section of the cutting-off head;

FIG. 4 is a circuit of the control unit.

The machine includes a bed 1 and a turn table 2 (FIG. 1) carrying allthe other assemblies. The guides 3 (FIG. 2) of the turn table 2 areprotected with a labyrinth packing 4. On the bed 1 there are mountedgrinding heads 5, polishing heads 6, cutting-off heads 7, drivesthereto, a drive to the table 2 and racks 8 (FIG. 1).

The construction of the grinding heads 5, polishing heads 6 andcutting-off heads 7 is accomplished in such a way that the grindingtools (baffing wheel and diamond cutting disc) are rotated from adirect-current motor through a drive 9 (FIGS. 2 and 3) and the head isoscillated through a link gear 10 from a d.c. motor provided with areduction gear.

Each of the grinding heads 5 and the polishing heads 6 has a body 11(FIG. 2) which is set on the tapered end of a hollow shaft 12 andoscillated in a sliding bearing 13 mounted in the bed 1. The body 11 andthe hollow shaft 12 are fixed by pins 14 and fastened between two thrustbearings 15 and 1.6 by means of a nut 17 having a stop screw.

The link gear 10 is fixed to the hollow shaft 12 with bolts 18. Thehollow shaft 12 mounted in radial bearings 19 and 20 comprises a shaft21 rotated through a pulley 22 and the drive 9 from a d.c. motor.

The rotary motion of the shaft 21 through a pulley 23, a V-shaped belt24, a tension roller 25 and a pulley 26 is imparted to a shaft 27carrying a buffing wheel 28. The shaft 27 is set in a sliding bearing 29which in turn is set in the body 11 through radial bearings 30 and 31.The shaft 27 carrying the buffing wheel 28 has a short play along theaxis of the bearing 29 due to a bayonet mechanism 32 and a frictionmechanism 33.

The buffing wheel 28 with a grinding portion flexibly mounted andbearing an abrasive coating at one of its ends is covered with a casing34. In the whole the head is covered with a casing 35.

The cutting-off head 7 has a body 36 set on the tapered end of a hollowshaft 37 which is oscillated in a sliding bearing 38 (FIG. 3) which inturn in set in the bed 1. k

The body 36 and the hollow shaft 37 are fixed by pins 39 and fastenedbetween two thrust bearings 40 and 41 by means of a nut 42 having a stopscrew 43. The link gear 10 (FIGS. 2 and 3) is fixed to the hollow shaft37 with bolts 44. The hollow shaft 37 set in radial bearings 45 and 46comprises a shaft 47 rotated through a pulley 48 and the drive 9 from ad.c. motor.

The rotary motion of the shaft 47 through a pulley 49, a V-shaped belt50, a tension roller 51 is imparted to a spindle 52 which carries adiamond abrasive disc 53 having an inner cutting edge.

A sliding bearing 54 with an adjustable play and a hollow body 52rotating therein are fastened with a nut 55 and a thrust sliding bearing56 in the body 36. The body 52, the bearing 59 and the special nut 55are provided with labyrinth packings 57 and 58.

For lubricating the friction surfaces, on the body 36 there is mounted alubricator 59, and for delivering cutoff plates from the cutting zone,inside of the body 52 there is provided a transporting means 60 firmlyfastened to the bed 1 with a bracket 61 (FIG. 1). The cutting-offdiamond disc 53 is covered with a casing 62 and in the whole the head iscovered with a casing 63 (FIG. 3).

On the turn table 2 there are positioned a number of carriages 64 withblanks, a control unit 65 (FIGS. 1 and 4) of the turn table andlubricators 66 for lubricating the table guides.

Adjacent to the machine there is located a control desk 67 accommodatingcontrol units of the motors to the heads and an ac transformer forfeeding the control unit 65.

The turn table 2 is rotated by a d.c. motor with a reduction gearthrough a steering knuckle.

The carriage 64 comprises the following main assemblies and parts: abase 68, a support 69, guides 70, a body 71 and a chuck 72 (FIGS. 2 and3).

The base 68 and the support 69 are rigidly fixed to the table 2 (FIG.1). The base 68 is provided with a threaded bush 73 in which one of theends of a screw 74 (FIG. 3) is fastened. The other end of the screw 74carries a bevel gear 75 fixed thereon by a key and rotated in a slidingbearing 76 which is set in the support 69. The gear 75 is covered with acasing 77. The screw 74 is hollow and internally threaded, the pitch ofthe internal thread being finer than that of the external. Inside of thescrew 74 a screw 78 is mounted one of its ends being threaded toreciprocate the threaded bush 73. The other end of the screw 78 issmooth and positioned in a bush 79 which is fixed to the base 68.

On the smooth end of the screw 78 there is secured a key and the bush 79is provided with a keyslot to prevent the screw 78 from turning.

On the screw 78 there is mounted a bevel bush 80 which is screwed upwith a nut 81. The guides 70 are rigidly fixed on the base 68 and servefor travel of the body 71 resting on rollers 82 and 83.

The construction of the roller 83 makes it possible to compensate theplay.

The body 71 is connected with the bevel bush 80 by means of a specialbevel bolt 84.

The body 71 mounts a d.c. motor with a reduction gear and an electricbreak for rotating the chuck 72.

The chuck 72 is rotated in radial bearings 86 and 87 mounted in the body71. To the inner side of the chuck 72 there is fixed a sleeve 88 withholes. Inside of the sleeve 88, opposite to the holes, on the body 71there is fixed a photoresistor 89 (FIGS. 2 and 3); on the outside of thesleeve 88 there is positioned a lamp 90. Into the chuck there arepressed a number of sliding bearings 91 which, under the action ofsprings 92 and a pusher 93 of an electromagnet, provide thereciprocating motion of an axle 94.

The axle 94 is provided with quick-detachable locks for mounting blanks95 to be treated.

For lubricating the axle 94, into the chuck 72 there are pressedlubricators 96.

The electric circuit involves an input unit 97 (FIG. 4) with powertransformers and a short-cricuit protection, adjustable thyristorrectifiers 98, 99, 100, and 101, a l2-position scaling unit 102, asix-position scaling unit 103, a magnetic starter 104, a mechanism forsuppying voltage to the motor of the turn table and to the control unit65 (FIG. 3).

The control unit 65 of the turn table 2 consists of a rectifier 105, al2-position circular counter 106, a four-position circular counter 107and trigger units 108, 109, 110, 111, 112, 113, 114 and 115 (FIG. 4).

The above'described machine operates as follows: the blanks 95 to betreated are put into the locks which are then fixed to the axle 94.Subsequently, a voltage is applied to the input unit 97 and therectifiers 98, 99, 100, and 101. From the rectifiers 90 and 99 thevoltage is applied to the motors of the cutting-off heads 7. At the sametime the voltage is applied through the starter 104 (FIG. 4) to the unit65, and from the rectifier 105 it is applied through the circularcounter 107 to the triggers 108 and 112. As the trigger operate, theelectromagnet 93 compresses the spring 92 and pushes out the axle 94with the lock which carries the blank 95 into the zone of thecutting-off head 7.

In executing an oscillating motion, the cutting-off head 7 cuts off aplate from the blank. The cut-off plate falls to the transporting means60 (FIG. 3) and is transported thereby from the cutting zone. As thecuttingoff is over, the cutting-off head '7 is returned to its initialposition and pushesthe end switch which operates the circular counter106 to trigger the tiggers 100 and 112, the latter, in turn, switch onthe electric motors 05 positioned in the carriages 64 which are oppositeto the cutting-off heads 7.

When the chuck 72 with the sleeve 88 having holes is rotated, the holesof the sleeve 08 occur to be displaced. As soon as the lamp 90 lightsthe photoresistor 89 through a hole, the triggers 108 and 112 operate,the motor 05 stops and the pusher 93 of the electromagnet pushes out thesubsequent blank 95 for cutting.

Following this order, the machine can cut all the blanks positioned inthe chuck. Then the l2-position scaling unit 102 triggers and the signalis fed to the starter 104 to turn the table 2, and the table 2 turns byone-eighth revolution.

On completion of turning the table 2, the signal is fed to the scalingunit 103 to switch on the electric motor of the grinding heads 5.Simultaneously with the electric motors 85 the electric motors of thecarriages 64 are switched on which are at this moment opposite to thegrinding heads 5 rotating the chuck 72.

The buffing wheel 28 starts rotating and simultaneously advancing in thesliding bearing 29, as the friction mechanism 33 is designed for acertain force of clamping the buffing wheel to the ends of the blanksbeing machined.

When such a force is provided, the sliding bearing 29 starts rotating inthe radial bearings 30 and 31. The grinding process begins. At the sametime the electromagnet with the pusher 93 is triggered through thetriggers 109 and 113, and the blanks on the carriage 64 (FIG. 3) facingthe cutting-off heads '7 are successively pushed out into the cuttingzone, where they are cut and transported as it is hereinbeforedescribed.

Following each of the signals from the scaling unit 102 to turn thetable 2, a signal through scaling unit 103 is applied to the electricmotors of the heads 5 and 6. The electric motors of these heads reverseand the buffing wheel 28 moves away from the chuck 72 by means of thebayonet mechanism 32 and the friction mechanism 33 thus turning thetable 2.

When turning the table by one-eighth revolution, the bevel gear 75engages the rack 8 which is located on the bed opposite to thecutting-off heads coincidently with the table run and is turned througha certain angle. Therewith, the gear 75 turns the screw 74 which, whilebeing screwed into the bush 73, removes the screw 78.

In its translational motion the screw 78 advances the body 71 of thecarriage 64 along the guides for a dis tance equal to the pitchdifference of the screws 74 and 78. The relationship of these values isdetermined by a necessary thickness of the plates to be cut and can beadjusted.

The process for the alternative switching-on of the other heads andcarriages is similar to that hereinbefore described.

When there comes a point of the simultaneous operation of all the headsand carriages it means that the machine runs under automatic conditions.

When the blanks are cut to the end the carriage 64 runs over the endswitch to produce a signal for switching off the machine.

The machine is switched off in the same order as it is switched on.

The body 71 of the carriage 64 is returned in its initial position bymeans of a detachable device.

The use of this novel machine with two cutting-off heads and sixgrinding-polishing heads makes it possible to increase the efficiency ingrinding, for example,

silicon blanks for the production of solar phototrans ducers by about 20times as compared to commercial machines designed for the same program,and provides considerable reduction of the floor areas necessary for theproduction as well as of the maintenance personnel.

Thus, for example, the productivity of labour with the use of thismachine in grinding silicon blanks 45-50 mm. in diameter is about 35sec. per plate, while with the use of the commercial devices it is about10 min. per plate.

What is claimed is:

1. A machine for the simultaneous machining of a plurality ofsemiconductor blanks, comprising: a bed; a turn table mounted on saidbed for moving in a circle; machining heads, including cutting-off,grinding and polishing heads, fixed about said table at identicalangular spaces from one another, the operative part of each of saidheads having means for oscillating about a first axis radially relativeto said table and means for rotating about a second axis radiallyrelative to said table; said means for imparting oscillating motion toeach of said heads comprising link gears with a shaft secured to saidbed; carriages with chucks to carry blanks, said carriages being mountedon said table at identical spaces from one another corresponding to theangular space between said heads, and means to impart reciprocatingmotion to said carriages toward said cuttingoff heads in a radialdirection, said reciprocating means being mounted on each of saidcarriages; means to rotate said chucks with blanks in the course ofmachining; a pusher attached to each of said carriages to feed theblanks in the opertive position to said cutting-off heads; and means toconvey the cut-off portions of said blanks, said conveying means beingmounted in each of said cutting-off heads.

2. A machine as claimed in claim 1, including a control unit and acounter to sequentially switch the operative units of the machine.

3. A machine as claimed in claim 2, wherein each of said chucks hasorificed sleeves and a photoelectric resistance for sending a signal tosaid counter to switch on and off the means for rotating said chucks andsaid said shafts for transmitting rotary motion to said heads.

1. A machine for the simultaneous machining of a plurality ofsemiconductor blanks, comprising: a bed; a turn table mounted on saidbed for moving in a circle; machining heads, including cutting-off,grinding and polishing heads, fixed about said table at identicalangular spaces from one another, the operative part of each of saidheads having means for oscillating about a first axis radially relativeto said table and means for rotating about a second axis radiallyrelative to said table; said means for imparting oscillating motion toeach of said heads comprising link gears with a shaft secured to saidbed; carriages with chucks to carry blanks, said carriages being mountedon said table at identical spaces from one another corresponding to theangular space between said heads, and means to impart reciprocatingmotion to said carriages toward said cutting-off heads in a radialdirection, said reciprocating means being mounted on each of saidcarriages; means to rotate said chucks with blanks in the course ofmachining; a pusher attached to each of said carriages to feed theblanks in the opertive position to said cutting-off heads; and means toconvey the cut-off portions of said blanks, said conveying means beingmounted in each of said cutting-off heads.
 2. A machine as claimed inclaim 1, including a control unit and a counter to sequentially switchthe operative units of the machine.
 3. A machine as claimed in claim 2,wherein each of said chucks has orificed sleeves and a photoelectricresistance for sending a signal to said counter to switch on and off themeans for rotating said chucks and said pusher to cut the blanks.
 4. Amachine as claimed in claim 1, wherein said grinding and polishing headshave a bayonet mechanism to press the grinding and polishing wheels witha given force to said blanks being machined and to withdraw said wheelsat the end of the process when said table is turned.
 5. A machine asclaimed in claim 1, wherein said link gears of the heads are mounted onhollow shafts secured to said bed, a spindle extending through each ofsaid shafts for transmitting rotary motion to said heads.